Devices such as electric motors, generators and transformers include a magnetically conducive base which is generally known as a “stator”. The stator includes a core and a winding. The winding is typically a copper winding which is located within the slots formed in the core.
Stators typically adopt either one of two basic geometries. The first geometry is known as “radial flux” and the second geometry is known as “axial flux”. In a stator having “radial flux” geometry, the flux that generates torque flows in a direction perpendicular to the axis of rotation. In a stator having “axial flux” geometry, the flux that generates torque flows in a direction parallel to the axis of rotation.
Devices including a stator adopting “axial flux” geometry are often referred to as “pancake” devices due to their flat round shape. In contrast, devices adopting “radial flux” geometry are typically drum shaped.
Devices adopting “axial flux” geometry have generally been considered to be advantageous. However, it is recognised that the manufacture of the magnetic core for such devices is difficult.
U.S. Pat. No. 2,356,972 describes a machine for constructing laminated cores for electrical devices. FIG. 1 illustrates the layout of the machine described in U.S. Pat. No. 2,356,972. Cores are formed using a punch and wind process whereby core forming material is punched with apertures and then wound onto a roll 2. To begin the process, the free end of the core forming material is bent at a 90° angle 3 and positioned in a locating slot 4 on the roll 2. The entire roll 2 is then rotated, drawing more material around itself, until a required rotation angle (that is the angle between successive slots in the core) has been achieved. An aperture is then punched into the material by a punch and die arrangement 6. This process is repeated until the desired roll size is achieved.
As illustrated in FIG. 1, the entire roll 2 is located upon a linear slider 7 which allows free vertical movement of the roll 2. Roller 10 ensures that the top of the roll 2 is always maintained at a set height and thus the spring 9 is compressed as the radius of the roll 2 increases.
It will be appreciated by those skilled in the art that the difficulty when producing this form of core is to ensure that the apertures are punched in the material so that they align properly to form the required “straight sided” radial slots. If the apertures are punched at an equal spacing the required “straight sided” slots will not be formed. To address this problem, the machine described in U.S. Pat. No. 2,356,972 includes a ramp 11. The ramp 11 presses against the roll 2 and is arranged to move the punch and die arrangement 6 horizontally away from the roll 2 as the radius of the roll 2 increases. Spring 12 ensures that the ramp 11 is continuously fixed against the roll 2. Brake 14 and guide rollers 13 ensure that the material is fed to the punch and die arrangement 6 in a controlled manner. The horizontal displacement of the punch and die arrangement 6 can, if correctly implemented, produce the required “straight sided” radial slots in the core. Unfortunately, this is not often possible because of the difficulty in maintaining the material between the punch and die arrangement 6 and the roll 2 in a horizontal orientation.
It will also be appreciated that as the punch displacement parts of the machine shown in U.S. Pat. No. 2,356,972 wear, the accuracy of the positioning of the aperture punched by the punch and die arrangement 6 will decrease, leading to malformed slots in the resultant core.
Although other forms of machines have been developed to manufacture cores with “straight sided” radial slots, they all suffer from a lack of precision with regard to the positioning of the punched apertures.
The present invention seeks to provide an improved punch and wind machine.